<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">hello</div>
</body>
</html>
<script>
    let data = {
        msg : 'hello',
        count:0
    }
    let vm = {}
    proxyData(data)
    function proxyData(data){
        Object.keys(data).forEach(key=>{
            Object.defineProperty(vm,key,{
                enumerable:true,
                configurable:true,
                get(){
                    return data[key]
                },
                set(newValue){
                    if(newValue === data[key]){
                        return
                    }
                    data[key] = newValue
                    document.querySelector('#app').innerHTML = data[key]
                }
            })
        })
    }

</script>